Case head expansion / teach me

[chet]

So, I'm loading for a friends 7mm rem mag. Nosler brass. Fired three times. Sized them last night (partial, bumping the shoulder .002") The case body gets sized to within about 1/16" of the belt. The gun is an elcheapo walmart push feed M70, and is far from a match grade chamber.
I noticed a tiny ridge where the die stopped near the belt, I can feel it with my fingernail. I still had a few pieces of un-fired brass so I got out the mic and started comparing. I'm at work now, and dont remeber the numbers, but the measurements seemed substantialy different. The outside diameter of the belt was quite a bit larger on the fired cases, as was the diameter of the un-sized portion of the body.
I feel that full length sizing will only weaken the case head (bad expeirience with a 243)
My questions are:
How much expansion is too much?
At which point do I disgard brass?
Should I just not worry about it until I see actual separation?
They all chamber fine, and no signs of pressure whatsoever.
thoughts?

 

[rick smith]

The cases have expanded to fit the chamber and contracted to the current dimention, not a problem. You will get seperation if you try to bring the cases back to original dimentions. Good time to anneal the necks. Until the cases get too snug to bolt closure or you detect incipent case head seperation, continue with your method.Rick.

 

[Stevesdl]

Just a few thoughts from a novice but learning real fast with reloading 338 win mag brass.

1. Sounds like you have the headspace discernment on the mark. OAL made a difference on my pressures as well so I backed off on the powder.
2. Quality Brass - I am starting to believe this makes a difference as well - I switched to Nosler Custom Brass

My research on reloading and brass life has on a number of occasions brought me to articles on magnum case bulge. I think this is what you might be talking about. I decided to see if a special custom reloading tool will make the difference. You use this tool only when you need it. I have only used it on a few rounds of 338 win mag brass on the 3rd reload so far.

Take a look at http://www.larrywillis.com/ regarding the Belted Magnum Collet Resizing Die. I will be able to review much better after a few more reloads but so far it worked as stated very nicely. The inventor is a pretty sharp reloader and will answer your questions if you want to give him a call.

I also purchased the Digital Headspace Gauge and my own personal opinion is that this device is rocket science and a tool well worth its cost.

Stevesdl

 

[rick smith]

Forgot to mention a tool that will help you find if you are having the beginning of case head seperation. Straighten out a paper clip and the bend a short 90 in one end. Slightly sharpen the end of the 90 bend. You can slide that into a case and feel for a indentation just above the web. If you find one, section the case above the indentation and look inside. If any of the cases show the indentation, scrape them. I usualy get ten or more firings from belted brass before I retire the brass.Rick.

 

[chet]

rick, thanks! these bulges are very minimal and in no way would I be able to feel it on the inside..... yet. maybe in the next few loadings.

steve, bear with me as I am horrible at putting my thoughts into text....
Using the collet to size the "buldge" would seem useful in sizing brass fired from a different chamber. However, I don't think It would be much help in this case. If these get to a point where they need the buldge reduced in order to chamber, I'd prefer to just scrap them. I'm thinking that the integrity of the webbing is compromised at that point, and separation is near. Also the collet die doesnt appear to address the enlarging belt????? It is a very educational read, however. And that headspace guage is BAD AZZ!!!!! I use a modified (by chet) collet on my stoney point OAL guage to measure headspace, however it does not allow me to measure a loaded round.

thanks guys, and keep em comin!!! :grin:

 

[chet]

also steve, you've just taught me why some of the 300wm brass shot from my dads 700 would never chamber well in my M70, no matter how "full length sized" they were :lol:
thanks

 

[rick smith]

Use the Stoney Point "Hornady" headspace gauges and you can measure a loaded round. Sinclair has gauges that fit the SP holder that do the same thing.Rick.

 

[hardpan]

+1 on larry's site.
http://www.larrywillis.com/

Great guy that really understands belted mags. For you, I think that you are beginning to see belt bulge. His die will help, and likely your brass will be ok in your gun. But, it may not fit in another gun of the same caliber.
Hardpan

 

[JD338]

Forgot to mention a tool that will help you find if you are having the beginning of case head seperation. Straighten out a paper clip and the bend a short 90 in one end. Slightly sharpen the end of the 90 bend. You can slide that into a case and feel for a indentation just above the web. If you find one, section the case above the indentation and look inside. If any of the cases show the indentation, scrape them. I usualy get ten or more firings from belted brass before I retire the brass.Rick.

Good point Rick. I have also done this and it works well. You will feel the thinning of the case wall.

JD338

 

[woods]

A case will expand to fit the chamber. Factory chamber can be larger or smaller than each other depending on the reamer size and how worn it is when your gun is reamed at the factory. The bulge you are talking about will also be determined by the size of the case head on the specific brand and lot number of brass you are using

Here is a pic of a 30-06 case with a bulge that does absolutely no harm

By contrast I have a 280AI from Hart that has such a small chamber that my die will not even size the case body, even when set to push the shoulder back.

If the case is expanding at the belt then you should be also losing the primer pockets. If the primer pockets are not expanding so they will not hold a primer then your pressure is not extreme. That does not mean you don't need to look for other pressure signs or follow the manuals.

Belted magnum cases have a problem that unbelted cases do not generally have. That is the fault of the gun manufacturers and the case manufacturers in equal parts. The gap at the shoulder of new belted magnum cases is always much larger than the gap at the shoulder of new unbelted cases. If you have a Headspace gauge that measures this like the Hornady then you can take measurements on the new case before firing and after firing to see how much of a gap there was.

For example on this Winchester 264 win mag

new cases

once fired cases

that is a huge difference of .038"!

This is not headspace since the forward movement of the case in the chamber was stopped by the front of the belt. Headspace was within acceptable limits of .007" as determined by the belt. But that headspace is not what determines how much the case expands forward to the shoulder and that excessive expansion is what causes the thinning at the web and eventual case head separations. Sure, once the case is fired you can headspace on the shoulder but most of the damage is done on the initial firing.

The Willis die is a good tool if it is needed. Personally I have never had a problem with chambering difficulties due to expansion at the pressure ring so have never needed it and I have reloaded for over 2 dozen different belted case rifles. If I ever run into the problem I would not hesitate to purchase one as I am sure it would work as advertised.

 

[chet]

very helpful guys!! thank you!

 

[chet]

here are some numbers:

new brass:
belt measures .528"
body just under belt .506"

once fired:
belt measures .529"
body just under belt .509"

thrice fired:
belt measures .529"
body just under belt .511"

primer pockets still feel tight, thrice fired brass needed to be trimmed (barely)

we'll see what the fourth firing does.

 

[Innovative]

Chamber clearance at the head. It's quite a story, and I've never seen it explained completely in ANY reloading manual. I recently made a professional quality video (DVD) that explains these items in detail - but simple terms. It includes 20 minutes reloading at the bench.

1.) How do case heads expand
2.) What can make them expand too much
3.) Why handloads don't always chamber
4.) How to eliminate headspace separation
5.) How to measure the bullet jump to your rifling
6.) How to set die height accurately
7.) Which is best FL or NK resizing & why
8.) How to reduce case run-out
9.) Best reloading techniques for reloading belted, rimmed and non-rimmed cases
10.) How to simplify precision reloading ....